Method of and device for detecting surface elevations in sheet material

ABSTRACT

A method of and device for detecting surface elevations, like lumps, wrinkles, creases, etc. in paper and other sheet material. The sheet material is made to pass over a supporting roll and feeler members are mounted in a movable manner at a small distance from the sheet material above the supporting roll. This distance is smaller than the surface elevations to be detected and electronic means are provided to give a signal when a surface elevation lifts the feeler member, thereby changing the distance between the feeler member and an independently pivoted reference member. Means are provided to keep the distance between the surface of the sheet material and the feeler members constant, independent of inaccuracies and eccentric running of the supporting roll by providing contact members which take bearing on the supporting roll either via the sheet material or on two smaller diameter end portions of the supporting roll. By tuning the mechanical oscillatory frequency of feeler members and reference members the device can be made insensitive to vibrations of the supporting roll.

llnited States Patent 1191 Urmenyi METHOD OF AND DEVICE FOR DETECTINGSURFACE ELEVATIONS IN SHEET MATERIAL [30] Foreign Application PriorityData Sept. 28, 1970 Great Britain 46,025/70 Mar. 4, 1971 Great Britain05,979/71 [52] US. Cl. 340/259, 33/147 N, 333/148 H, v 73/159; ZOO/61.13

511 Int. Cl. .I'Tifib 51706 [58] Field of Search 340/259; 33/148, 33/147N, 148 H; 73/159; ZOO/61.13

[56] References Cited UNITED STATES PATENTS l/l968 Scharf et al 340/259X 3/1970 Beebe 340/259 X 1/l97l Urmenyi 340/259 Primary Examiner-DavidL. Trafton Oct. 2, 1973 [5 7] ABSTRACT A method of and devicefordetecting surface elevations, like lumps, wrinkles, creases, etc. inpaper and other sheet material. The sheet material is made to pass overa supporting roll and feeler members are mounted in a movable manner ata small distance from the sheet material above the supporting roll. Thisdistance is smaller than the surface elevations to be detected andelectronic means are provided to give a signal when a surface elevationlifts the feeler member, thereby changing the distance between thefeeler member and an independently pivoted reference member. Means areprovided to keep the distance between the surface of the sheet materialand the feeler members constant, independent of inaccuracies andeccentric running of the supporting roll by providing contact memberswhich take bearing on the supporting roll either via the sheet materialor on two smaller diameter end portions of the supporting roll. Bytuning the mechanical oscillatory frequency of feeler members andreference members the device can be made insensitive to vibrations ofthe supporting roll.

1 Claim, 4 Drawing Figures SlGA/AL OUTPUT Patented 0a. 2, 1913 3,763,483

2 Sheets-Sheet 1 as 23 3a 4 23 Fig.1.

Patented Oct. 2, 1973 3,763,483

2 Sheets-Sheet 2 AMPL/F/E/Q SIG/V4 L 01/77 0 T METHOD OF AND DEVICE FORDETECTING SURFACE ELEVATIONS IN SHEET MATERIAL Several devices have beenproposed to detect surface elevations like lumps, creases, etc., inmoving paper and other sheet material in which the paper is made to passover a supporting roll and feeler members are mounted on a beam abovethe roll, the feeler members being positioned at a small distance abovethe surface of the paper adjacent to the area where the paper is incontact with the supporting surface, the said small distance beingsmaller than the smallest surface elevation to be detected and when asurface elevation is passing under a feeler member the feeler member islifted up by it momentarily and electronic means are provided to give afault signal every time one of the feeler members is thus lifted.

It will be appreciated that in order to obtain consistent andsatisfactory operation the supporting roll must be made to the highestdegree of accuracy. Such rolls are very expensive to make and a certainamount of inaccuracy always remains. More particularly it is impossibleto achieve perfect concentric running. Due to eccentric running thedistance between the feeler members and the surface of the sheetmaterial changes periodically with every revolution of the roll. Thecross section is not perfectly circular but is slightly oval and thiscontributes further to the periodic change in the distance between thefeeler members and the surface of the sheet material.

According to the invention the device for detecting surface elevationsin sheet material moving over a supporting roll which has a supportingsurface of cylindrical shape adapted to support the sheet material to beinspected, comprising at least one feeler member which is adapted to bemounted in a movable manner at a distance which is, smaller than thesmallest surface elevation to be detected, which distance may be zero,from the surface of the sheet material, opposite the area in which thesheet material is in contact with the supporting surface, part of thesurface of the feeler member being adapted to contact the surfaceelevations to be detected, a contact member mounted in a movable mannerand adapted to take a bearing on the supporting roll, a reference membercontrolled by the contact member and electrical means adapted to providean electrical signal when the feeler member is moved relative to thereference member by a surface elevation in the sheet material to beinspected.

In one example of the invention the contact member is placed adjacent tothe feeler member adapted to contact the surface of the sheet materialthus taking a bearing on the surface of the supporting roll via thesheet material.

In another example of the invention two contact members are adapted tocontact the supporting roll outside the supporting surface at the twoends of the supporting roll, a datum beam being mounted on the twocontact members essentially parallel to the supporting roll, thus thedatum beam taking a direct bearing on two portions of the supportingroll and the reference members are controlled by the contact members viathe datum beam.

The said two portions of the supporting roll are preferably of smallerdiameter than the diameter of the supporting surface. The said twoportions and the larger diameter supporting surface must be ground inthe same operation. The cross section of the supporting surface is nevera mathematically accurate circle but it is slightly oval. The crosssection of the smaller diameter portions, if ground in the sameoperation, will then also be slightly oval, having the same main axis,but the two cross sections will be equidistant to a great degree ofaccuracy and this is the only essential requirement.

The invention will now be more fully explained by way of examplesillustrated in the drawings in which:

FIG. 1 shows an example of a probe design including the contact member.

FIG. 2 shows diagrammatically an example of the mounting of the datumbeam.

FIG. 3 shows diagramatically the relative positions of the carrier beamwith probe, the datum beam and the supporting roll.

FIG. 4 shows an example of the invention in which a part of the electricmeans is mounted on the datum beam. I

In FIG. 11 of the drawing, 1 is a feeler member comprising also part 2which is a capacitor plate and is pivoted at points 24 and 26 usingcross strip hinges which for the sake of clarity of the drawing are notshown. Bracket 20, which carries the whole probe assembly, is adjustablymounted on a beam not shown. The weight of parts l and 2 is partiallybalanced by adjustable spring 21. 33 is a reference member pivoted atpoints 34 and 35. 4 is a capacitor plate mounted on part 33 by means ofinsulating members 23. 30 is a bracket carrying leaf spring 31 andadjusting screw 32. 36 is a bracket mounted on part 2 and is resting atpoint 37 on leaf spring 311. The weight of reference member 33 ispartially balanced by adjustable spring 38. 3 is a contact membermounted on bracket 25 which is pivoted at 28 and is biased by spring 39towards the supporting surface not shown. Part 25 carries a leaf spring43 which acts as a shock absorber. Instead of a leaf spring, a rubberpad may be used, both being the simplest types of shock absorbers, butare in many cases sufficient to reduce sudden shocks as they aretransmitted from member 3 to member 33. In some cases the use of a shockabsorber may be omitted, in other cases any of the known types of moreefficient shock absorbers may be used. Part 33 rests on part 25 viaadjustable screw 41 and leaf spring 40. 42 is an electrical wireconnection to insulated capacitor plate 4i.

In operation, contact member 3 is made to contact the surface of thesheet material to be inspected as it passes over a supporting surfacewhich in this case is a rotatable idler roll. By adjusting screw 32 theclear gap between capacitor plates 2 and 4 can be adjusted. Then byadjusting screw 41 plates 2 and 4 can be raised or lowered together,screw All being adjusted so that there is a small distance betweenfeeler member l and the sheet material to be inspected, said smalldistance being smaller than the smallest surface elevation to bedetected. When a surface elevation, which is greater than said distance,is passing under member ll, member 1 is lifted thereby reducing thedistance between capacitor plates 2 and 3 producing thus an electricalsignal.

In order to be able to detect limp creases, adjustable spring 21 must beadjusted so that the greater part of the weight of parts ll 2 isbalanced so that a very small force is only required to lift theseparts. If parts 1 and 2 are deflected and then left to themselves, theywill carry out mechanical oscillations, the frequency of theseoscillations depending on the adjustment of spring 21. If the supportingsurface is subjected to vibrations, these vibrations are transferred tocontact member 3 and via screw 41 to member 33. Normally this wouldcause changes in the gap between parts 2 and 4 and produce unwantedfault signals. Now if spring 38 is adjusted so that the naturalmechanical oscillatory frequency of parts 4 and 33 is equal to theoscillatory frequency of parts 1 and 2, then every time part 33 is movedupwards via screw 41 due to the vibration of the supporting surface,part 2 is also moved upwards by part 33 via leaf spring 31 and contactpoint 37, and the two parts 2 and 33 move up and down together, keepingthe gap between 2 and 4 unchanged and so no electrical signal isproduced.

Theoretically of course it would be possible to mount the contact memberdirectly on member 33 and the same effect would be achieved. However, itwill be appreciated that if spring 21 is adjusted so that a very smallforce is required to lift parts 1 2, or in other words bracket 36 restson leaf spring 31 with a very small force, then if spring 38 is adjustedso that the frequency of mechanical oscillations of part 33 is equal tothe frequency of mechanical oscillations of part 2, the force by whichpart 33 rests via screw 41 on part 25 is also very small. If contactmember 3 would be mounted on member 33, then the pressure of part 3 onthe sheet material would be very light and part 3 would not rotate butwould skid over the surface of the sheet material, thereby collectingdirt, and in case of coated paper collecting coating material. In orderto ensure that part 3 is safely rotated by the moving sheet material,part 3 is mounted on a separate pivoted member 25 which is biased byspring 39 towards the sheet and the supporting surface to provide thenecessary pressure. Alternatively, if member 25 has sufficient weight,the pressure can be provided by the weight of part 25 alone without theuse of spring 39.

In practice the machanical oscillations of parts 2 and 33 is of veryshort duration and consists usually of one period of oscillation only,due to the contact between screw 41 and arm 25, via shock absorber 40 ifone is used. Therefore the mechanical tuning of parts 2 and 33 is notcritical and often good results can be achieved if part 33 is tuned to ahigher frequency than part 2.

Usually more than one probe is used, since the length of member 1 cannot be made long enough to inspect the whole width of the material to beinspected. The lengths in the radial direction of parts 2 and 25 may bealternately varied so that part 1 of one probe extends in front orbehind part 3 of the neighbouring probe, thereby parts 1, essentiallyend to end, inspect the whole width of the material.

If it is required that the contact members should contact the supportingroll outside the supporting surface, then arm 25 is omitted andreference member 33 is resting via adjusting screw 41 on bracket 49 ofthe datum beam (see FIG. 3).

In FIG. 2, 42 is the supporting roll, 43 is one of the said two portionsof the supporting roll, 44 is the datum beam pivoted at 45 and taking adirect bearing on portion 43 via pad 46, the said pad being made of amaterial of low coefficient of friction, e.g., porous bronze impregnatedwith PTFE, 47 is an adjustable balancing weight, 48 is a compressionspring, which may be made adjustable if so required, 49 is a bracket, 50is a removable gauge piece. Parts 43, 45 to 48 and 50 are duplicated atthe other end of the supporting roll 42 and beam 44, not shown in thedrawing. Pivoting points 45 are preferably in the plane tangential to 43at the point of contact with 46.

In FIG. 3, 51 is the sheet material to be inspected. Identical parts aredenoted with the same reference numerals as in the previous Figures.Adjusting screw 41 is resting on bracket 49. For the sake of clarity ofthe drawing brackets 30 and 36 have been omitted from this figure.

In FIG. 4, identical parts are again denoted with the same referencenumerals as in the previous Figures. Here capacitor plate 4 is mountedon bracket 49. The distance between plates 2 and 4 is adjustable bymeans of adjusting screw 52. The distance between feeler member 1 andthe surface of the sheet material may be adjusted by adjusting screw 41.If required, adjusting screw 41 may be omitted, and feeler member 1allowed to contact the surface of the sheet material. In the latter casea rotating roller may be used as feeler member instead of a stationaryrod.

By reasons of mechanical design the length of feeler member 1 islimited. If the width of the sheet material to be inspected is greaterthan the length of a single feeler member, then several probes may bemounted on the carrier beam next to each other so that the feelermembers extend over the whole width of the sheet material. If more thanone feeler member is employed, an equal number of brackets 49 must beprovided or alternatively one long bracket may be used extending overthe whole length of beam 44.

In operation gauge pieces 50 of suitable thickness must be insertedaccording to the thickness of the sheet material and the desireddistance between the feeler members and the sheet material whichdistance may be zero. The balancing weight or weights 47 and/or spring48 must be adjusted to obtain the smallest possible pressure betweenparts 43 and 46 compatible with the speed of the roll. The higher thespeed of the roll, the greater must be this pressure to ensure thatparts 43 and 46 do not lose contact. At low speeds springs 48 areomitted and at very high speeds balancing weights 47 are omitted andsprings 48, which may be arranged to provide adjustable spring pressure,are applied.

At low speeds it is possible to arrange for the datum beam to rest viapad 46 on the supporting surface itself, but at high speeds this hasseveral practical disadvantages. First of all it is inconvenient becauseshould the sheet material accidentally run out sideways it could damagethe precision contacting surface of pad 46. Then the braking torque ofthe datum beam on the roll is greater on the larger diameter, and theadditional braking torque due to the inertia forces of the beam whilstit is accelerated upwards every half cycle of eccentric running is alsogreater; When the braking torque reaches a certain critical value, whichdepends on the angle of lap of the sheet material over the roll and thecoefficient of friction between the sheet material and the roll, thesheet material is unable to rotate the roll and skids over the roll. Incases of certain types of sheet material, especially when the materialis thin, the sheet material tears before the critical braking torque isreached. For all these reasons there is a great technical advantage tobe gained by providing smaller diameter cylindrical portions 43 forsupporting the datum beam and for thin or weak materials and/or at highspeeds this is the only practical solution. At very low speeds however,satisfactory results may be obtained when the datum beam takes bearingon the supporting surface.

When a surface elevation is passing under feeler member 1, the feelermember is lifted up thereby reducing the distance between plates 2 and4, increasing the electrical capacitance between them and thusinitiating an electrical signal. It is clear that when due to eccentricrunning of roll 42 or its non-circular cross section datum beam 44 islifted up, bracket 49 lifts up plate 4 by the same amount, which in turnlifts up plate 2 and feeler member 1 via leaf spring 31 and bracket 36by an equal amount. Since due to the method of manufacture, as explainedabove, the surfaces of 43 and 42 are equidistant, i.e., the radialdistance between 43 and 42 is constant round the circumference, thedistance between feeler member 1 and the upper surface of the sheetmaterial 51 remains constant and equally the distance between plates 2and 4 remains unchanged.

Various modifications may be made to the above example without departingfrom the invention. For example parts 46 may be replaced by precisionball races. Alternatively ball races may be mounted on parts 43 and thedatum beam adapted to rest on the stationary outer parts of the ballraces. Instead of pivoting the datum beam at 45, it may be mounted forlinear vertical movement using, e.g., linear ball bearings. Thefunctions of the carrier beam and the datum beam may be united in onesingle beam at low speeds. However since the beam would carry the weightof the probes it would have to be of a more rigid and therefore heavierconstruction. The combined weight of the heavy beam and of the probeswould be very much greater than the weight of a separate light weightdatum beam, in consequence the pressure and therefore the frictionaltorque on the supporting roll would greatly increase which, at highspeed, would become prohibitive. The probe design of FIG. 1 is only oneof many possible designs and any probe design capable of giving anelectrical signal may be adapted for use in conjunction with theinvention. For example, the feeler member 1 in FIG. 2 may be a rollerrotated by a small motor mounted on plate 2 and a brush or cleaning padmounted nearby contacting the roller (or a jet of air directed at theroller) cleans it continuously in order to remove dust particles whichmay accummulate on it. Alternatively, the feeler member ll, being aroller, may be adapted to contact the sheet material and be rotated byit. In the latter case brackets 30 and 36 and parts 311, 32 and 37 wouldbe omitted. Eccentric running and oval cross section of roll 42 wouldcause roll l to rise and fall periodically with every revolution of roll42, but reference member 33 would also rise and fall due to similar riseand fall of beam 44 and in consequence the gap between capacitor plates2 and 4 remain constant except when roll 1 is lifted by a surfaceelevation in the sheet material. In all examples capacitor plates 2 and4 may be replaced by any other electrical means capable of giving anelectrical signal when one part moves relative to the other, e.g.,electromagnetic inductive means. Wheels 3 or pads 46 may be replaced bymembers suitably shaped to enclose an air cushion which could besustained by the continuous supply of air under pressure. Thus directmechanical contact with the sheet material or with parts 43 of thesupporting roll would be avoided.

I claim:

1. Device for detecting surface elevations in sheet material moving overa supporting roll (42) which has a supporting surface of cylindricalshape comprising at least one feeler member adapted to be mounted in amovable manner opposite the area in which the sheet material is incontact with the supporting surface, at a distance, which is smallerthan the smallest surface elevation to be detected, which distance maybe zero, from the surface of the sheet material, the feeler member (11)being adapted to contact the surface elevations to be detected, at leastone contact member (3) mounted in a movable manner adapted to take abearing on the supporting roll, a reference member (33), the position ofwhich relative to the surface of the sheet material is controlled by thecontact member (3), adjustable means (411) being provided, controlled bythe contact member (3), which prevents the distance between thereference member (33) and the surface of the sheet material becomingless than a pre-set value, and adjustable means (32) being providedwhich prevent the distance between the reference member (33) and thefeeler member (ll) becoming more than a preset value, and electricalmeans adapted to produce and electrical signal when the feeler member(l) is moved relative to the reference member (33) by a surfaceelevation in the sheet material.

i ll 4 =0 *l

1. Device for detecting surface elevations in sheet material moving overa supporting roll (42) which has a supporting surface of cylindricalshape comprising at least one feeler member adapted to be mounted in amovable manner opposite the area in which the sheet material is incontact with the supporting surface, at a distance, which is smallerthan the smallest surface elevation to be detected, which distance maybe zero, from the surface of the sheet material, the feeler member (1)being adapted to contact the surface elevations to be detected, at leastone contact member (3) mounted in a movable manner adapted to take abearing on the supporting roll, a reference member (33), the position ofwhich relative to the surface of the sheet material is controlled by thecontact member (3), adjustable means (41) being provided, controlled bythe contact member (3), which prevents the distance between thereference member (33) and the surface of the sheet material becomingless than a pre-set value, and adjustable means (32) being providedwhich prevent the distance between the reference member (33) and thefeeler member (1) becoming more than a pre-set value, and electricalmeans adapted to produce and electrical signal when the feeler member(1) is moved relative to the reference member (33) by a surfaceelevation in the sheet material.